I. Field of the Invention
This invention relates generally to a machining lathe, and more particularly to a split frame clamshell-type portable machining lathe for cutting and finishing relatively large diameter pipes.
II. Description of the Prior Art
Split frame clamshell lathes of the type described herein are known in the art. My earlier U.S. Pat. Nos. 4,739,685 and 4,939,964 are illustrative of the technology involved. The split frame pipe machining lathe generally comprises first and second semicircular halves that are designed to be joined together so as to surround the pipe to be machined. The resulting annular assembly includes a stationary ring portion that becomes clamped to the pipe and an abutting rotatable portion including a ring gear that is journaled to the stationary portion for rotation about the concentrically disposed pipe. An air-operated, hydraulically-operated or electrically-operated motor is operatively coupled to the assembly and includes a drive gear designed to mesh with the ring gear on the rotatable segment of the pipe lathe. Also mounted on the rotatable segment of the pipe lathe is a tool block for supporting a cutting tool that can be made to advance in the radial direction against the pipe to be machined in incremental steps upon each revolution of the ring gear.
A problem has heretofore existed in the prior art in the manner in which the ring gear has been journaled to rotate relative to the stationary clamping ring. It FIG. 2 of my earlier U.S. Pat. No. 4,739,685, which is reproduced herein as FIG. 1, there is shown a cross-section illustrating the manner in which the gear member 10 is journaled for rotation relative to the stationary ring member 11. A first set of roller bearings 12 cooperate with the straight arcuate surface of a circular race member 14, which is bolted onto the ring gear member 10 by bolts 13. The race member 14 also cooperates with a second set of bearings 15. The bearings in set 15 have opposed beveled segments for cooperating with a W-shaped surface 16 formed on the race member 14 and with a V-shaped extension or protuberance 17 formed on the inner side wall of the cavity 18.
It has been found that under load, the race member 14 behaves like a fulcrum, allowing the ring gear 10 to rock back and forth which results in undue wear on the bearings and slight variation in the cutting circle as the ring gear orbits the pipe being finished. Moreover, the assembly is costly to manufacture because of the intricacies in the machining required to produce the ring gear 10 and the tolerances that need to be maintained between the ring gear 10 and the circular race member 14 so that these parts will provide the appropriate contact with the associated bearings 12 and 15.
In the low clearance pipe lathe described in my earlier U.S. Pat. No. 4,939,964, the problems inherent in the journaling of the ring gear to the stationary member described in the '685 patent were partially resolved. FIG. 2 herein taken from the '964 patent shows the way the ring gear is journaled in that earlier invention. The problem of undue wear occasioned by the ability of the ring gear 19 therein to rock under loads was still present. Again, the race member 20 was fabricated separately from the ring gear 19 and affixed to it by bolts which made it difficult to maintain the desired degree of contact between the race member 20, the W-shaped segment 21 on the ring gear and the notched roller bearings 22 affixed to the stationary member 23.